Studies on activity-induced re-organization of the PSD complex were continued. Experiments on the regulation of an abundant PSD component, AIDA-1, by CaMKII were concluded and published (Dosemeci et al, FEBS Lett 2016). In this study, isolated PSDs were used to demonstrate phosphorylation of AIDA-1 upon activation of PSD-associated CaMKII. In parallel experiments, by immuno-electron microscopy, CaMKII inhibitor, tatCN21 was observed to block NMDA-induced movement of AIDA-1 out of the PSD core in hippocampal neurons. CaMKII-mediated redistribution of AIDA-1 is similar to that observed previously for SynGAP. We hypothesize that CaMKII-mediated removal of these two abundant PSD-95-binding proteins from the PSD core may open a window of opportunity for the trafficking of glutamate receptors during synaptic activity. As a first step in studying the dynamics of synaptic cleft components that bridge the pre- and postsynaptic compartments, we needed to identify proteins that are selectively localized at the synaptic cleft. Although cell adhesion molecules enriched in synaptosomal fractions are typically classified as synaptic cleft components, some of these proteins may be partly or exclusively located on peripheral membranes surrounding the synaptic cleft. Thus, we devised a strategy to obtain a fraction enriched in synaptic junctions devoid of peripheral membranes. The protocol involved limited phopholipase A2 treatment of synaptosomal fractions to selectively remove peripheral synaptosomal membranes. N-Cadherin, Neuroligins, Neurexins and SALM5 were found to be enriched in these phospholipase A2-derived preparations, suggesting preferential localization at the synaptic junction, whereas other presumptive cleft components, including SALM2, SALM3, EphrinB ligand, EphA4 receptor, NCAM and SynCAM were not, suggesting a more diffuse distribution. The predictions from biochemical studies were verified by immuno- electron microscopy for some of the proteins, including neuroligins, NCAM and SynCAM. The cytoplasmic surface of the PSD abuts the actin cytoskeleton of the dendritic spine. Two actin-binding proteins, Cortactin and Abp1, can also bind PSD scaffold proteins of the Shank family, and thus may function as a bridge between the PSD and the adjoining actin cytoskeleton. Activity-induced changes in the distribution of these proteins may underlie coordinated changes between the PSD and actin cytoskeleton. Preliminary immuno-electron microscopy studies indicated localization of Abp1 at the PSD, as well as elsewhere within the neuronal cytoplasm. Confirming a previous study, cortactin label was observed to be dispersed within the spine cytoplasm, with a subpopulation inside the PSD complex. Ongoing studies aim to explore activity-induced changes in the localization of these two proteins.